This invention relates to aromatic silane compounds and to Ziegler-Natta catalyst systems which use said aromatic silane compounds as electron donors for the production of olefin polymers. The olefin polymers produced with such catalyst systems exhibit a desirable stereoblock content of from about 7 to about 25%.
Polymer stereoblock content can affect the physical properties of the polymer itself and those of products prepared therefrom, particularly films manufactured from such polyolefins and blends of such polyolefins with elastomeric materials, regardless of whether they are mechanically blended from pre-produced polyolefins and elastomeric materials or reactor blended by first producing such a polyolefin then producing the elastomeric material in the presence of the polyolefin.
Organosilane compounds have been used in catalysts (1) as an internal electron donor in a solid catalyst component comprising a halogen-containing titanium compound supported on an activated magnesium dihalide compound and (2) as an external electron donor in combination with an aluminum-alkyl co-catalyst. Typically the organosilane compounds have Sixe2x80x94OR, Sixe2x80x94OCOR or Sixe2x80x94NR2 groups, where R is alkyl, alkenyl, aryl, arylalkyl or cycloalkyl having 1 to 20 atoms. Such compounds are described in U.S. Pat. Nos. 4,180,636; 4,242,479; 4,347,160; 4,382,019; 4,435,550; 4,442,276; 4,473,660; 4,530,912 and 4,560,671, where they are used as internal electron donors in the solid catalyst component; and in U.S. Pat. Nos. 4,472,524, 4,522,930, 4,560,671, 4,581,342, 4,657,882 and European patent application Nos. 45976 and 45977, where they are used as external electron donors with the aluminum-alkyl co-catalyst.
Conventional propylene homopolymers, obtained by using external electron donors known in the state of the art, show a high degree of cristallinity, which determines the physical properties of the polymers, such as high melting temperature, high glass temperature and high xcex94Hfus. These physical properties, while necessary in some applications, are often disadvantageous in fiber and film applications, where lower bonding temperatures are required, for instance in producing laminate structures.
Hence, there is the need for external electron donor compounds which allow propylene polymers to be obtained having a relatively high degree of stereoblocks, at the same time at acceptable polymerization yields.
It has been surprisingly found that a novel class of substituted aromatic silane compounds can be used as external electron donors for olefin polymerization catalyst systems, in order to produce propylene polymers having a stereoblock content of from about 7 to about 25%.
In one aspect, the present invention concerns an aromatic silane compound useful as electron donor compound in an olefin polymerization catalyst, having formula (I): 
wherein
R1 is selected from the group consisting of linear or branched C1-26 alkyl, C2-26 alkenyl, C1-26 alkoxy, C2-26 alkoxyalkyl, C7-26 arylalkyl, C3-26 cycloalkyl and C4-26 cycloalkoxy groups, optionally containing one or more halogen atoms;
R2 is an aromatic ring having at least one substituent in the ortho position selected from C1-10 hydrocarbon groups; and
R3 and R4, the same or different from each other, are selected from the group consisting of a linear or branched C1-10 alkyl and C3-10 cycloalkyl groups.
In another aspect, the present invention concerns a catalyst system for the polymerization of olefins comprising:
(A) an aromatic silane compound having formula (I): 
wherein
R1 is selected from the group consisting of linear or branched C1-26 alkyl, C2-26 alkenyl, C1-26 alkoxy, C2-26 alkoxyalkyl, C7-26 arylalkyl, C3-26 cycloalkyl and C4-26 cycloalkoxy groups, optionally containing one or more halogen atoms;
R2 is an aromatic ring having at least one substituent in the ortho position; and
R3 and R4, the same or different from each other, are selected from the group consisting of a linear or branched C1-10 alkyl and C3-10 cycloalkyl groups;
(B) an aluminum alkyl compound; and
(C) a solid catalyst component comprising Mg, Ti, halogen and an electron donor compound.
In another aspect, this invention concerns a process for the polymerization of alpha-olefins carried out in the presence of the catalyst system described above, to produce a polyolefin having a stereoblock content of from about 7 to about 25%, and preferably from 12 to 20%.
The inventors have discovered that organosilanes having an aromatic ring substituted in the ortho position can produce, in conjunction with the catalyst systems described below, polyolefin resins having a stereoblock content of from about 7 to about 25%.
The aromatic silane compounds of the present invention have the following formula (I): 
wherein R1, R2, R3 and R4 have the meanings reported above.
In one preferred embodiment of the present invention, R1 is a linear or branched C1-18 alkyl or C3-18 cycloalkyl, and even more preferably R1 is a linear C1-5 alkyl or a branched C3-8 alkyl.
R2 is an aromatic ring having at least one substituent in the ortho position selected from C1-10 hydrocarbon groups. Depending on the stereoblock content desired, R2 may preferably be a non-heterocyclic aromatic system, and most preferably a mono-substituted phenyl ring system, a di-substituted phenyl ring system, or a mono-substituted naphthyl ring system. By xe2x80x9csubstituent in the ortho positionxe2x80x9d, it is meant that at least one of the two aromatic ring atoms adjacent to the aromatic ring atom that is bound to the silicon atom must be substituted.
The groups R3 and R4, the same or different from each other, are preferably C1-10 alkyl, and even more preferably are methyl or ethyl.
Illustrative examples of aromatic silanes which conform to formula (I) include the following:
(2-ethylphenyl)-3,3-dimethylbutyl-dimethoxysilane;
(2-ethylphenyl)-3-methylbutyl-dimethoxysilane;
(2-ethylphenyl)-propyl-dimethoxysilane;
(2-ethylphenyl)-3,3,3trifluoropropyl-dimethoxysilane;
(2-methylphenyl)-propyl-dimethoxysilane; and
(2,6-dimethylphenyl)-propyl-dimethoxysilane.
The aromatic silanes of the present invention may be prepared from readily available starting materials using conventional synthesis methods and equipment well known to those of ordinary skill in the art. Aromatic silanes where the aromatic ring system is an ortho-substituted phenyl group may be prepared by the reaction between the appropriate 2-phenylmagnesium bromide and the appropriate alkyl-trialkoxysilane, as illustrated in Example 2. Alternatively, such ortho-substituted aromatic silanes may be prepared by first reacting the appropriate 2-bromobenzene with an alkyl lithium reagent, such as n-butyl lithium, to generate the corresponding 2-phenyl lithium, which is then allowed to react with the appropriate alkyl-trialkoxysilane, as illustrated in Example 3.
The organosilanes of the present invention are useful as the external electron donor in an olefin polymerization catalyst system. More particularly, the present invention concerns a catalyst system for the polymerization of olefins comprising:
(A) an aromatic silane compound having formula (I): 
wherein
R1 is preferably a linear or branched C1-18 alkyl or C3-18 cycloalkyl, and even more preferably R1 is a linear C1-5 alkyl;
R2 is an aromatic ring having at least one substituent in the ortho position;
R3 and R4, the same or different from each other, are preferably C1-10 alkyl groups, and even more preferably are methyl or ethyl;
(B) an aluminum alkyl compound; and
(C) a solid catalyst component comprising Mg, Ti, halogen and an electron donor compound as essential elements.
In said aromatic silane compound (A), R1 is preferably selected from the group consisting of linear or branched C1-18 alkyl, C1-18 alkoxyl and C3-18 cycloalkyl groups, and even more preferably R1 is selected from the group consisting of linear C1-5 alkyl and branched C3-8 alkyl groups. R2 is preferably selected from the group consisting of mono-substituted phenyl, di-substituted phenyl and mono-substituted naphthyl, and the ortho substituent is preferably a linear or branched C1-10 alkyl or C1-10 alkoxy group. R3 and R4 are preferably selected from the group consisting of linear or branched C1-8 alkyl and C3-8 cycloalkyl, and even more preferably are methyl or ethyl.
The aluminum alkyl compound (B) may be triethylaluminum, isobutylaluminum, tri-n-butylaluminum, and linear and cyclic alkylaluminum compounds containing two or more aluminum atoms linked to one another through oxygen or nitrogen atoms or SO4 or SO3 groups. Examples of such alkyl aluminum compounds include (C2H5)2Alxe2x80x94Oxe2x80x94Al(C2H5); (C2H5)2Alxe2x80x94N(C6H5)xe2x80x94Al(C2H5); (C2H5)2Alxe2x80x94SO2xe2x80x94Al(C2H5); CH3[(CH 3Alxe2x80x94Oxe2x80x94]nAl(CH3)n; and (CH3Alxe2x80x94Oxe2x80x94]n. The alkyl aluminum compound (B) is preferably triethylaluminum.
The solid catalyst component (C) preferably comprises a titanium compound having at least one titanium-halogen bond and an internal electron donor, both supported on an active magnesium halide.
The titanium compound, which may be selected from titanium tetrahalides and titanium alkoxy halides, is supported on the solid magnesium halide, according to common procedures.
The titanium compound is preferably TiCl4.
The magnesium halide is in anhydrous state, and preferably has a water content of less than 1% by weight. The magnesium halide is preferably MgCl2 or MgBr2, with MgCl2 being most preferred.
Those of ordinary skill in this art are well aware how to activate the magnesium dihalide compound, and to determine its degree of activation. More particularly, the active magnesium halides forming the support of component (C) are the Mg halides showing in the X-ray powder spectrum of component (C) a broadening of at least 30% of the most intense diffraction line which appears in the powder spectrum of the corresponding inactivated magnesium halide having 1 m2/g of surface area or are the Mg dihalides showing an X-ray powder spectrum in which said most intense diffraction line of the inactivated magnesium dihalide is absent and is replaced by a halo with an intensity peak shifted with respect to the interplanar distance of the most intense diffraction line and/or are the Mg dihalides having a surface area greater than 3 m2/g.
The measurement of the surface area of the Mg halides is made on component (C) after treatment with boiling TiCl4 for 2 hours. The value found is considered as the surface area of the Mg halide.
The Mg dihalide may be preactivated, may be activated in situ during the titanation, may be formed in situ from a Mg compound, which is capable of forming Mg dihalide when treated with a suitable halogen-containing transition metal compound, and then activated, or may be formed from a Mg dihalide C1-3 alkanol adduct wherein the molar ratio of MgCl2 to alcohol is 1:1 to 1:3, such as MgCl2.3ROH where R is a C1-20 linear or branched alkyl, C6-20 aryl or C5-20 cycloalkyl.
Very active forms of Mg dihalides are those showing an X-ray powder spectrum in which the most intense diffraction line appearing in the spectrum of the corresponding inactivated magnesium halide having 1 m2/g of surface area is decreased in relative intensity and broadened to form a halo or are those in which said most intense line is replaced by a halo having its intensity peak shifted with respect to the interplanar distance of this most intense line. Generally, the surface area of the above forms is higher than 30-40 m2/g and is comprised, in particular, between 100-300 m2/g.
Active forms are also those derived from the above forms by heat-treatment of component (C) in inert hydrocarbon solvents and showing in the X-ray spectrum sharp diffraction lines in place of halos. The sharp, most intense line of these forms shows, in any case, a broadening of at least 30% with respect to the corresponding line of inactivated Mg dihalides having 1 m2/g of surface area.
The internal electron donor may be selected from alkyl, aryl, and cycloalkyl esters of aromatic acids, especially benzoic acid or phthalic acid and their derivatives, such as ethyl benzoate, n-butyl benzoate, methyl p-toluate, methyl p-methoxybenzoate, and diisobutylphthalate. Alkyl or alkaryl ethers, ketones, mono- or polyamines, aldehydes and phosphorus compounds, such as phosphines and phosphoramides, can also be used as the internal electron donor. The phthalic acid esters are most preferred.
Solid catalyst component (C) can be prepared using techniques and equipments well known to those of ordinary skill in the art. For example, the magnesium halide, titanium compound and the internal electron donor can be milled under conditions where the magnesium halide is active. The milled product is then treated one or more times with an excess of TiCl4 at a temperature of from 80xc2x0 to 135xc2x0 C. and then washed with a hydrocarbon such as hexane until all chlorine ions have been removed.
Alternatively, the solid catalyst component (C) may be prepared by first preactivating the magnesium chloride according to known methods, reacting it with an excess of TiCl4 containing the internal electron donor in solution at a temperature of from 80xc2x0 to 135xc2x0 C., and then washing the solid with a hydrocarbon such as hexane to remove residual TiCl4.
Yet another method for preparing the solid catalyst component (C) includes reacting a MgCl2nROH adduct (where R is a C1-20 linear or branched alkyl, C6-20 aryl or C5-20 cycloalkyl), preferably in the form of spheroidal particles, with an excess of TiCl4 containing the internal electron donor in solution at a temperature of from 80xc2x0 to 120xc2x0 C., isolating the solid, reacting it once more with TiCl4 and then washing the solid with a hydrocarbon, such as hexane, to remove all remaining chlorine ions.
The molar ratio between the Mg dihalide and the halogenated Ti compound supported thereon is preferably between 1 and 500, while the molar ratio between the halogenated Ti compound and the internal electron donor supported on the Mg dihalide is preferably between 0.1 and 50. The amount of aluminum alkyl compound (B) employed is generally such that an aluminum/titanium ratio is from 1 to 1000.
The catalyst system comprising an aromatic silane compound (A), an aluminum alkyl compound (B) and a solid catalyst component (C) can be added to the polymerization reactor by separate means substantially simultaneously, regardless of whether the monomer is already in the reactor, or sequentially if the monomer is added to the polymerization reactor later. It is preferred to premix components (A) and (B), then contact said premix with component (C) prior to the polymerization for from 3 minutes to about 10 minutes at ambient temperature.
The alpha olefin monomer can be added prior to, with or after the addition of the catalyst to the polymerization reactor. It is preferred to add it after the addition of the catalyst.
Another object of the instant invention is a process for the polymerization of alpha-olefins carried out in the presence of the catalyst system as described above.
The polymerization reactions can be done in slurry, liquid or gas phase processes, or in a combination of liquid and gas phase processes using separate reactors, all of which can be done either by batch or continuously.
The polymerization is generally carried out at a temperature of from 0 to 150xc2x0 C., and preferably from 40 to 90xc2x0 C.; the polymerization may be carried out at atmospheric pressure or at higher pressures, preferably from 100 to 10,000 kPa, and more preferably from 200 to 8,000 kPa.
Chain terminating agents, such as hydrogen, can be added as needed to reduce the molecular weight of the polymer, according to methods well known in the state of the art.
The catalysts may be precontacted with small quantities of olefin monomer (prepolymerization), maintaining the catalyst in suspension in a hydrocarbon solvent and polymerizing at a temperature of 60xc2x0 C. or below for a time sufficient to produce a quantity of polymer from 0.5 to 3 times the weight of the solid catalyst component.
This prepolymerization also can be done in liquid or gaseous monomer to produce, in this case, a quantity of polymer up to 1000 times the catalyst component weight.
Suitable alpha-olefins which can be polymerized by this invention include olefins of the formula CH2xe2x95x90CHR, where R is H or C1-20 straight or branched alkyl, such as ethylene, propylene, butene-1, pentene-1,4-methylpentene-1 and octene-1.
The aromatic silane compounds of the present invention, as well as the polymerization catalyst systems containing them, enable the production of propylene polymers, and in particular propylene homopolymer having a stereoblock content of from about 7 to about 25%, and preferably from 12 to 20%, by changing the ortho substituent on the aromatic ring of the silane themselves.
Propylene polymers prepared using the external electron donors of the present invention may be manufactured into films using conventional apparatus and techniques well known to those of ordinary skill in the polyolefin art.